We are engaged in trying to isolate and characterize the proteins involved in DNA replication in E. Coli. Towards this end we have isolated two multienzyme complexes capable of synthesizing DNA. For activity, one of these complexes requires single stranded DNA, Mg ions, the four ribonucleoside triphosphates, and the four deoxyribonucleoside triphosphates. This complex is inhibited by rifamycin, ara CTP and nalidixic acid. The other multienzyme complex we are studying requires double stranded DNA, Mg ions, ATP and the four deoxynucleoside triphosphates. Inhibitors of this complex include ara CTP, nalidixic and actinomycin. Rifamycin does not give any inhibition of enzymatic activity in this case.